The story follows a Roman architect named Lucius, who is having trouble coming up with ideas. One day, he discovers a hidden tunnel underneath a spa that leads him to a modern Japanese bath house. Inspired by the innovations found there, he creates his own spa, Roma Thermae, bringing in the modern ideas to his time.

In ancient Rome, bathhouse architect Lucius (Hiroshi Abe) becomes famous with designing the original "thermae" (bathhouse). He receives an order to build a thermae in the colosseum to help gladiators recover from their wounds, but faces difficulties. Thus, Lucius travels again to modern day Japan through the time slip. He meets Manami (Aya Ueto) again, who is now a reporter for a magazine which covers bathroom. With the help of the flat face Japanese tribe, Lucius again designs a new thermae. Meanwhile, Emperor Hadrian (Masachika Ichimura) wants to keep the peace with the thermae, but the Senate wants to extend the land by using force. Emperor Hadrian and the Senate now have a confrontation and Rome becomes divided.